1. Field of the Invention
The present invention pertains to the field of semiconductor memory technologies, relates to a method for manufacturing a dynamic random access memory and in particular, relates to a method for manufacturing a semi-floating gate device.
2. Description of Related Art
Semiconductor memories are widely used in many electronic products. There are different requirements for the construction, performance, and density of the semiconductor memory in different application fields. For example, a static random access memory (SRAM) has a very high random access speed and a relatively low integration density, while a standard dynamic random access memory (DRAM) has a very high integration density and a moderate random access speed. Currently, with the continuous expansion of the market demand for semiconductor memories, the processes and methods for manufacturing dynamic random access memory technologies are innovated and many problems which restrain the process for manufacturing dynamic random access memory products are being solved.
Chinese Patent Application No. 201310119651.8 proposes a U-shaped channel semiconductor device and a manufacturing method thereof. A sectional structure of the U-shaped channel semiconductor device along a length direction of a current channel is as shown in FIG. 1. The memory device includes a source region 201, a drain region 202, and a U-shaped channel region 401 formed in a semiconductor substrate 200, and a first layer of insulating film 203 and a floating gate 205 which is used as a charge storage node and provided with a notch formed above the drain region 202 and the U-shaped channel region 401. A p-n junction diode is formed between the floating gate 205 and the drain region 202 via a floating gate opening region 204. A second layer of insulating film 206 and a control gate 207 are formed, covering the source region 201, the floating gate 205, and the p-n junction diode structure, and in a length direction of a channel of the device, the control gate 207 isolates the source region 201 from a top of the floating gate 205 on a top of the formed U-shaped groove.
A method for manufacturing the U-shaped channel semiconductor device includes: after forming a U-shaped groove, first removing a hard mask layer 301, further forming a first layer of insulating film 203 on the surface of the U-shaped groove and a semiconductor substrate, and then forming a floating gate opening region 204 in the first layer of insulating film 203 on a side wall located on a top of the U-shaped groove and close to one side of a drain region 202, as shown in FIG. 2; subsequently, further forming a floating gate 205, as shown in FIG. 3. The process procedures of forming a floating gate opening region 204 in the first layer of insulating film 203 on the side wall located on the top of the U-shaped groove and close to one side of the drain region 202 are complex, manufacturing is rather difficult, and it is difficult to control and ensure quality of finished products of the semiconductor device.